Statement of Problem: Evaluation of fracture properties is a basic principle for true assessment of brittle materials’ properties. Resin–based composite materials are being used extensively in today’s dentistry. Fracture toughness is considered an important parameter for providing useful information about material’s nature, properties and its resistance to fracture.

Purpose: The purpose of this study was to evaluate the fracture toughness of a resin composite produced in the country and to compare it with that of other standard materials.

Materials and Methods: Four types of resin composite materials were used as follow to prepare 60 specimens (n=15 for each group), A) Tetric Ceram (Ivoclar–Vivadent); B) Brilliant (Coltene-Whaledent); C) SpectrumTPH (Dentsply); and D) Ideal Macoo (Ideal Macoo, Iran). Specimens of 5 mm diameter ( 0.1 mm) and 2 mm depth (±0.1 mm) were prepared in a central notch (90 notch angle) PTFE mold. Then specimens were light cured with two applications of overlapping exposures for a total of 120 s and were stored in distilled water at 37ºC for 48 hours, A cylindrical roller of 3 mm diameter was seated inside the V sections and fracture was accomplished in a universal testing machine at a crosshead speed of 0.5 mm/min. Data were analyzed by one–way ANOVA and post-hoc paired Tukey HSD test with P<0.05 as the limit of significance.

Results: The mean KIC and torque to fracture (T) values for each material tested were; A) 3.080.42, 16.992.34, B) 2.880.63, 16.041.98; C) 3.400.53, 18.752.93 and D) 2.870.46, 15.782.57 MN/m3/2SD and N/mmSD, respectively. Group C showed significantly the highest mean KIC and T values among groups tested which was significantly higher than that of group B and D (P<0.05). The mean KIC and T values for groups A, B, and D were not significantly different (P>0.05).

Conclusion: From evaluating the fracture properties of materials tested in this study it was concluded that the mean fracture toughness value for SpectrumTPH (Dentsply) was significantly higher than that of Ideal Macoo resin composite material (Ideal Macoo, Iran). The F.T value for Ideal Macoo was considered acceptable as it was not significantly different from that of other resin composite materials tested.